I have successfully installed and synchronised Ethereum Wallet and it has correctly brought in my test Ether purchase. How do I resynchronise to ensure more current transactions are recorded on my account?
I've noticed the same thing on one of my machines. (Running Mist 0.7.3 and Geth 1.4.x or 1.5, on Linux Mint [which is Debian-based and presumably should just work].)
I believe there's actually a bug here. Mist should keep itself synchronised, but isn't doing.
Similar behaviour was reported in this previous thread. Though the main topic of that thread was not being able to send Ether, the OP reported that Mist wouldn't continue to sync once opened.
Edit: See this bug report.
If you have to run Geth again, don't forget to specify
--cache, such as
geth --cache=1024. It will help, especially when you have not synced for a while and have many blocks to download.